Alzheimer's disease (AD) affects more than 12 million patients worldwide, accounting for most dementia diagnosed after the age of 60. The disease is clinically characterized by a global decline of cognitive function that progresses slowly and leaves end-stage patients bedridden, incontinent and dependent on custodial care; death occurs, on average, nine years after diagnosis (Davis et al., in Pharmacological Management of Neurological and Psychiatric Disorders, pp. 267-316, 1998). In addition to its direct effects on patients, advanced AD puts a tremendous burden on family caregivers and causes high nursing home costs for society. Age is the major risk factor for AD, and a health care crisis is likely in countries with aging populations if treatments that protect against the disease or delay or stop its progression cannot be introduced within the next decade. The current standard of care for mild to moderate AD includes treatment with acetylcholine-esterase inhibitors to improve cognitive function (Doody, R., Alzheimer Dis. Assoc. Disord., 13:S20-S26, 1999). These drugs are safe, but of limited benefit to most patients.